A known valve timing control apparatus disclosed in JPH10-220207 includes a rotation transmitting member to which rotational power is transmitted from a crankshaft pulley and mounted on a rotational shaft portion for opening and closing a valve so as to be relatively rotatable within a predetermined range, a vane attached to the rotational shaft portion configured by a camshaft and an inner rotor provided integrally with the camshaft, an operating chamber defined by the rotational shaft portion and the rotation transmitting member and divided into an advanced angle chamber and a retarded angle chamber by the vane, a first fluid passage formed in fluid communication with the advanced angle chamber for supplying and discharging a fluid therein and therefrom, respectively, a second fluid passage formed in fluid communication with the retarded angle chamber for supplying and discharging the fluid therein and therefrom, respectively, a retracting bore formed at the rotation transmitting member for housing a locking pin being biased by a spring toward the rotational shaft portion, a receiving bore formed at the rotational shaft portion and into which a head portion of the locking pin is inserted when a relative phase between the rotational shaft portion and the rotation transmitting member is synchronized to a predetermined phase and a third fluid passage formed in fluid communication with the receiving bore for supplying and discharging the fluid therein and therefrom.
According to the valve timing control apparatus disclosed in H10-220207, the fluid communication through the third fluid passage is established independently from the fluid communication through each of the first fluid passage and the second fluid passage.
In the foregoing structure, because the fluid communication through the third fluid passage is established independently from the fluid communication through each of the first fluid passage and the second fluid passage, for example, whenever the internal combustion engine is in operation, from its start to stoppage, but not at immediately after the start of the engine in which the rotation is unstable, the oil may be stably supplied in a continual manner to the receiving bore via the third fluid passage, and during the time period immediately after the start of the internal combustion engine and upon the stoppage thereof, the fluid can be drained from the receiving bore.
Thus, while the internal combustion engine is operated, but not immediately after the start of the internal combustion engine, the head portion of the locking pin can retract into the retracting bore after leaving the receiving bore and the locking pin can remain in the unlocked state. In addition, during the time immediately after the start of the internal combustion engine and upon the stoppage thereof, the head portion of the locking pin is inserted into the receiving bore for maintaining the locking condition.
However, when the internal combustion engine is stopped, a position of the locking pin may not correspond to a position of the receiving bore. In this case, the locking pin may be moved so as to be inserted into the receiving bore by use of small oscillating movements of the camshaft caused by torque fluctuation. According to the valve timing control apparatus in H10-220207, a switching valve for supplying/discharging the fluid to/from the third fluid passage and a control valve for supplying/discharging the fluid to/from the first fluid passage and the second fluid passage are arranged so as to be parallel to the pump, and the fluid is supplied to the first fluid passage or the second fluid passage at the time of the start of the internal combustion engine, and then the chambers are filled with the fluid so that the small oscillating movements of the camshaft may not occur, accordingly the locking pin may not be inserted into the receiving bore.
A need thus exists to provide a valve timing control apparatus which is not susceptible to the drawback mentioned above.